I'm testing upconverting and donwconverting a DSB-SC signal using two diode ring mixers in a fixture that connects both mixers with a matching network.
The first mixer has 81Mhz at LO, 100kHz at IF and an amplifier at RF. If I put a 50 ohm load at the amplifier output, the DSB signal looks as expected:
![](/proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FkaL8Z.png&hash=c273f5f3c343a39cb8983f7aa9353b0a)
The amplifier has Zo=40+20j and the mixer has Zi=0.5+80j. The mathing network I'm using has a 20p shunt capacitor (matching 40+20j to 50 ohm) followed by an L section (matching 50 ohm to 0.5+80j).
If I connect both mixers with that network, the signal gets very distorted before and after the network:
![](/proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FFa9l9.png&hash=34c3cd5f40d47eeb641a5e54596c2228)
If I remove the low pass filter at the downconverting mixer IF port and replace it by a 50 ohm load, it has a very large impact on the signals:
![](/proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2F58AvV.png&hash=1f19c3c77cd8b01ddb19fec3e31f200a)
The mathing network seems to be working, because if I remove it:
![](/proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FJXD14.png&hash=d8d4a49f058bc566e7bf6d65df7ad966)
Someone can help me deciphering what's going on? Is this mathing network ok? If not, how is it done? Are those impedances well calculated?
Thanks in advance![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
The first mixer has 81Mhz at LO, 100kHz at IF and an amplifier at RF. If I put a 50 ohm load at the amplifier output, the DSB signal looks as expected:
![](/proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FkaL8Z.png&hash=c273f5f3c343a39cb8983f7aa9353b0a)
The amplifier has Zo=40+20j and the mixer has Zi=0.5+80j. The mathing network I'm using has a 20p shunt capacitor (matching 40+20j to 50 ohm) followed by an L section (matching 50 ohm to 0.5+80j).
If I connect both mixers with that network, the signal gets very distorted before and after the network:
![](/proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FFa9l9.png&hash=34c3cd5f40d47eeb641a5e54596c2228)
If I remove the low pass filter at the downconverting mixer IF port and replace it by a 50 ohm load, it has a very large impact on the signals:
![](/proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2F58AvV.png&hash=1f19c3c77cd8b01ddb19fec3e31f200a)
The mathing network seems to be working, because if I remove it:
![](/proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FJXD14.png&hash=d8d4a49f058bc566e7bf6d65df7ad966)
Someone can help me deciphering what's going on? Is this mathing network ok? If not, how is it done? Are those impedances well calculated?
Thanks in advance
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